This invention is directed to a process and a system for the production of scrambled eggs. More particularly, process and the system of the invention are directed to producing homogeneous scrambled eggs with a homogenous firmness while minimizing channeling and fouling of holding tubes used to cook the egg product.
Producing scrambled eggs having a homogeneous firmness at high volumes without channeling or fouling cooking equipment or damaging heating equipment as a result of the fouling has been a problem. During the initial heating of the eggs with a heat exchanger such as a scraped surface heat exchanger, egg has fouled the heat exchanger even to the extent of breaking the heat exchanger blades.
Holding tubes where liquid egg is held at elevated temperatures to cook the eggs develop xe2x80x9cchannelingxe2x80x9d. This is where laminar flow develops, as egg thickens and/or coagulates at the outer boundaries of the holding tube but tends to stay liquid at the center. In this circumstance egg flows faster through the center of the holding tube than at the outer perimeter, and as a result, develops a center channel. This creates a product which is not evenly cooked. For instance, egg flowing through the center channel tends to be undercooked, resulting in a watery or mushy egg product. At the same time, egg at the outer boundaries of the holding tube tends to be overcooked, resulting in very small pieces. The typical approach for minimizing laminar flow and eliminating large distributions of residence time in a hold tube is to induce turbulent flow. Turbulence is usually induced by creating high flow velocities or by providing mechanical shear (e.g. in a screw extrusion cooker). This is not acceptable in the production of scrambled egg product, however, as the solid and partially coagulated egg is very shear sensitive, as excessive shear leads to a finely granulated product with poor mouth feel.
It is an object of this invention to provide a continuous process for making scrambled egg product which is homogeneous in firmness and which is evenly cooked.
It is another object of this invention to provide a process and system for making evenly cooked scrambled egg product having a homogeneous firmness where the process will also minimize the fouling and channeling in the equipment used to cook the egg product.
These and other objects of the invention will become apparent with reference to the following summary and description.
The present invention is directed to a process for the production of scrambled egg product and a system for practicing the process of the invention. The process and system maximizes scrambled egg product consistency and/or firmness homogeneity and minimizes channeling, fouling and equipment wear previously associated with the production of scrambled eggs. Maximization of egg product homogeneity and/or consistency and minimization of channeling and fouling is provided by periodically interrupting the flow of egg through the system of the invention. Flow interruption is achieved by stopping and starting the flow of heated liquid egg product in the holding tube effective for providing a discontinuous flow of heated egg product in the holding tube. This reduces laminar flow of the heated egg product in the holding tube compared to a laminar flow of heated egg product which would develop in the holding tube without the stopping and starting.
With elimination and/or control of egg channeling in holding tubes where egg is cooked, the process of the invention eliminates or controls undercooking of the eggs and mushy texture that results from insufficient or non-uniform cooking. The process provides scrambled egg product that is sufficiently cooked to allow egg protein to coagulate and provide scrambled egg product having a homogeneous firmness of from about 20 mm to about 50 mm (as hereinafter defined) as it exits the holding tube where it is cooked. Further, it has been observed that overcooking of the egg product and/or subjecting the cooked egg product to significant shear results in an unacceptably large quantity of fines (small particles) in the final product. The process described in the invention avoids the production of these fines by minimizing the opportunity for xe2x80x9cthermal shockxe2x80x9d (the development of significant thermal gradients), and ensuring that the velocity, and hence residence time, of egg product in the holding tube is more uniform.
In accordance with the process of the invention, liquid egg product is first heated to a temperature less than a cooking temperature for the egg, but the temperature being sufficiently high to prevent heat shock of the liquid egg product and prevent non-uniformity in the scrambled eggs produced by the process and system of the invention. The initially heated egg then is further heated to provide a homogeneously heated egg product. This additional or further heating brings the egg to a temperature which is effective for cooking the egg product and effective for causing the heated liquid whole egg product to coagulate when the liquid egg product is held in a holding tube downstream from the area of the additional heating. This brings the egg product to a cooking temperature to provide a cooked egg product with an apparent viscosity greater than about 1500 centipoises as measured with a Brookfield viscometer with a spindle No. 5 and a constant spindle speed of 20 revolutions per minute. After the egg product is brought to a cooking temperature it is transported to a holding tube. The homogeneously heated egg product is held in the holding tube at the cooking temperature for an amount of time effective for forming a fully coagulated and cooked egg product. The flow of egg product in the holding tube is stopped and started to provide a discontinuous flow of the homogeneously heated liquid egg product in the holding tube. This stopping and starting is effective to significantly reduce the velocity gradient where egg at the center of the tube moves faster than egg at the outer periphery of the tube; and hence, reduces the range of residence times experienced by the cooked egg flowing through the holding tube as compared to the flow pattern that could be expected to develop in the holding tube with continuous feed. After cooking, the fully coagulated cooked egg product is removed from the holding tube. The process and system of the invention may be used to process and cook liquid whole egg, as well as liquid egg product as defined herein.
The initial heating of the egg product brings cool egg from temperatures such as about 39xc2x0 F. (or about 4xc2x0 C.) to a temperature in the range of from about 130xc2x0 F. to about 154xc2x0 F. in about 1 to about 25 minutes, preferably about 5 to 25 minutes. This eliminates thermal shock to the egg when brought to cooking temperature, which shock will cause a rapid and sudden coagulation of at least some part of the egg. This will ultimately cause a non-uniform coagulation and cooking of the egg product in the holding tube.
During the initial heating, the egg product may increase to a viscosity of from 100 cps to about 1500 cps (Brookfield viscometer with a spindle No. 5 and a constant speed of 20 rpm measured at 25xc2x0 C.). The initial heating may be accomplished using any type of heat exchanger as known in the art for this purpose, such as a tube in tube pre-heater.
After the initial heating, the initially heated liquid egg product is further heated as uniformly as possible to bring the egg product to a cooking temperature before it is transported to a holding tube for cooking. If the egg is brought to temperature with a hot surface, a significant thermal gradient should not be allowed to develop. To this end, a scraper can be used to continuously refresh the material at the hot surface with cooler material from the bulk of the egg in the heating device. Alternatively, local turbulence may be induced in the heating device, without causing significant turbulence downstream, by using pulsed flow through the heat exchanger. The hot liquid egg is much less shear sensitive than the completely or partially coagulated material, and so acceptable product can be produced despite the level of shear induced during heating.
Uniformity of the heating and avoidance of a large temperature gradient in the egg product ultimately effects the homogeneity of firmness of the egg product exiting the holding tube. Hence, the measures used to minimize thermal gradients during the final heating step should be sufficient and effective for providing the egg product exiting the holding tube with a homogeneous firmness in the range of from about 20 mm to about 50 mm when the egg product also is subjected to the discontinuous flow as described in this application.
In one aspect of the invention, steam is injected into the egg product to further and homogeneously heat the egg product to a cooking temperature in the range of about 163xc2x0 F. to about 175xc2x0 F. The steam generally is injected at a pressure of from about 5 psi to about 40 psi. The steam injection is immediately followed by a shear-inducing step such as, in the preferred embodiment, a pump. The injection of the steam and operation of the downstream mixing device is done in a manner, rate and pressure that is effective for maintaining a homogenous product with a uniform and homogeneous firmness in the range of from about 20 mm to about 50 mm, preferably about 25 mm to about 45 mm as the egg product exits the holding tube. The steam temperature generally ranges from about 240xc2x0 F. to about 270xc2x0 F.
When liquid egg product is transported into the holding tube and the flow of product through the holding tube is interrupted or stopped then started, the product has a residence time in the holding tube effective for providing the firmness described above which is generally about 8 to about 15 minutes being cooked at a temperature range of about 163xc2x0 F. to about 175xc2x0 F.
The process of the invention may be batch or can be continuous, even with one holding tube. A reciprocating pump can provide the interruption or stoppage of the flow of egg product through a system with one holding tube. In a system with one hold tube, a device that allows a near continuous feed while providing a discontinuous output may be introduced between the heating and holding parts of the process. A device such as a reciprocating pump may be used for this purpose. In an important aspect, multiple holding tubes may be used to make the process continuous with the flow of homogeneously heated egg product in one holding tube continuing while the flow of egg product in at least one other tube is stopped. In a preferred aspect, the process and system of the invention has two insulated holding tubes. In this aspect of the invention, the homogeneously heated liquid egg product is transported into one of the holding tubes. A flow control regulator or valve switches the flow of homogeneously heated egg product from a first holding tube then to a second holding tube and then back to the first tube at intervals which push product through the tube, but allow product to reside in the tube to cook the egg and provide the egg product with a homogeneous firmness of at least about 50 mm or keep the egg product in the tube for the times and temperatures indicated above. Alternatively, product may be pumped through more than two tubes at appropriate intervals to effect discontinuous flow through the tubes.
After exiting the holding tube(s), fully coagulated or cooked egg product may be extruded to form a homogeneous scrambled egg product having the firmness in the range of from about 20 mm to about 50 mm. The scrambled egg product may be immediately frozen and packaged or may be mixed with other food items and then frozen and packaged.
In another aspect, the invention further provides a continuous system for producing scrambled eggs. The system includes a holding tank effective for providing liquid whole egg product. The liquid whole egg product is transported to a heat exchanger which is effective for initially heating the liquid egg product to a temperature of not more than about 154xc2x0 F. and to prevent heat shock of the liquid egg product in subsequent processing steps.
The system of the present invention may further include a steam inlet effective for providing an injection of steam at a temperature and pressure sufficient to raise the egg product to a temperature at which cooking can occur, followed by a device to impart significant mixing and increase in pressure, such as a Silverson Shear pump, effective for ensuring that the steam energy is provided homogenously to the egg mixture. The pump provides the environment that insures that the heat from the steam is rapidly dispersed within the liquid egg product, thereby avoiding thermal shock. Further, the downstream pump provides part of the backpressure needed to force material through the hold tube, thereby allowing the steam to be introduced at a lower pressure (temperature) than would otherwise be possible. The steam injection and subsequent pump are operated in a manner effective for evenly heating the liquid egg product to a cooking temperature which will cook the egg product in the holding tube(s) as described above. In an important aspect, the steam heated liquid egg product has a temperature in the range of from about 163xc2x0 F. to about 175xc2x0 F. The system of the invention includes a means for controlling the flow of steam heated egg product, such as a reciprocating pump or valve, to at least one holding tube, and preferably at least two holding tubes. Egg product is maintained in the holding tube(s) at a time and temperature effective for forming a fully coagulated or cooked egg which has a uniform firmness in the range of from about 20 mm to about 50 mm when it exits the holding tube. The scrambled egg product from the holding tube then is extruded through an extruder.